1. Technical Field
This invention relates to an improved rope clamp of the smallest possible size and one in which the holding strength or efficiency is not dependent upon the skill of fabricating personnel, and, more particularly, to a rope clamp for the terminating end of a composite rope having a metallic core and an outer sheath of fibrous plastic material, or made from multi-layered plastic materials. Such composite rope normally has a multi-strand metallic core surrounded by one or more outer sheaths of fibrous plastic material comprising a lightweight line capable of carrying heavy loads, which rope is widely used by rescue workers, firemen and in various safety applications. The rope is also frequently used in certain military and marine applications, the rope being resistant to severing, chemicals, shock and the like, and is also resistant to destruction by high temperatures such as may be encountered in fires or explosions. The subject rope clamp may also be used with a rope comprised of several separately-braided layers of fibrous plastic materials without the multi-strand metallic core.
A primary purpose of this invention is to meet the military and commercial requirements for a rope end clamp, and which satisfies all of the following requirements for the termination of fibrous synthetic and composite synthetic ropes:
(1) The outer diameter being as near as possible to that of the rope.
(2) A rope clamp that will hold the full strength of the rope.
(3) A rope clamp whose holding strength is consistent and does not vary in large amount from one clamp to another.
(4) A rope clamp whose holding strength is not dependent upon the ability of assembly personnel.
The herein-disclosed embodiments of the subject rope clamp utilize a unique combination of wedging elements and proven assembly techniques for a new and unique design of outer swagged-type of rope end clamp.
2. Background Information
Previously, composite ropes fabricated of both metallic and plastic materials into multi-layered flexible lines have been well-known for use in survival-type situations as well as in mountaineering and other hazardous conditions. Their use in such hazardous conditions has been limited by their inherent nature such as in the event of fire or high-temperature applications. The nylon, polyester or other synthetic materials used in the manufacture of such ropes may melt or burn, or may be so severely weakened by heating that the rope becomes unsafe for further use. Such composite ropes having a metallic core are not easily knotted around stable fixtures and require an improved terminating end clamp to join the rope to a suitable fitting such as a clevis or other connecting member. U.S. Pat. No. 1,855,227 to Fiege discloses a single wedging plug employed in an inner conical recess to clamp a metallic cable to a clevis or turnbuckle. Such clamp is not applicable to use with a composite rope formed of different layered materials, such as one having a metallic core surrounded by plastic sheaths.
Composite ropes which are subjected to applications where they come into contact with rock outcropping or other sharp objects, such as in mountaineering or fire fighting, may be severed or partially severed since the synthetic plastic materials utilized in their outer construction are not highly resistant to chafing and severing. Further, if the outer plastic sheath be severed or partially severed, the multi-layer construction allows the individual outer layers to slip along the inner metallic core or move axially relative to one another making the line difficult to grasp or properly handle.
It is also known that exposure to chemicals can also degrade the rope and ultimately cause its failure. Ropes which have been subjected to such exposure are frequently discarded and not used further as a precautionary measure if subjected to any corrosive chemicals. This may be true where chemicals are found on the ground where the rope has been lying and been exposed to such chemicals.
A further disadvantage of conventional multi-layer composite rope, particularly when used in rescue and safety applications, is its elasticity. While a conventional rope experiences a certain degree of stretch when under load, undue elasticity of a composite rope may adversely affect various rescue and safety operations. The use of a metal cable core avoids the problem of line loss due to heat, fire and severing problems. Composite ropes or cables, due to their elasticity, are difficult to tie and otherwise manipulate due to their flexible but unwieldy nature. In most cases a knot cannot be safely tied in the cable which will cinch tightly enough on itself to hold and provide safe connection of the line and it is normally difficult to increase the diameter of the cable by doubling it to facilitate grasping of the cable due to weight and other considerations. When a metal cable is employed, its outer surface is frequently too slippery to be securely grasped presenting an unsafe condition and is sometimes too abrasive to be handled safely depending upon the used condition of the cable. Various types of knotting of the cable at its end to various metallic fittings has not been satisfactory since the metallic core and outer sheaths may slide axially with respect to one another resulting in an unsafe condition.
Previously, the fastening of cable ends together or the securing of a single composite cable end to a support has encountered considerable difficulty. Where a strong joint is required at the line end, where the rope is fully fabricated having a metallic core, the line in some cases has been welded to connecting members requiring the use of heating apparatus which is destructive of the sheath of plastic material. Various clamping devices have been utilized but such devices have been found to withstand only very limited strain and do not clamp both the metallic core and the outer plastic sheath by separate clamping elements.
Previously the most efficient method of terminating textile ropes has been the "hand splice". Such method relies on the ability and experience of the assembly personnel, has a large variation of holding efficiencies from one clamp to another, and does not provide a satisfactory termination for a synthetic fibrous rope having an internal metallic wire core. A chemically potted termination has a high holding efficiency but is dependent upon the assembly technique and is very large in size. The internal wedge of "Fiege" type clamp is strong, does not rely on assembly proficiency of the fabricating personnel, but is still relatively large in size. The "swagged" type of end clamp can not normally be employed on synthetic textile-type ropes as it can on wire ropes, since the textile or fibrous nature of the rope reduces in diameter with tensile loading and pulls out of a termination that relies on compressive loading alone to hold the rope.
Another type of end clamp for a composite rope has been disclosed in pending U.S. patent application Ser. No. 07/518,572 filed May 3, 1990 now U.S. Pat. No. 5,022,780 entitled "End Clamp for Textile Rope With a Metallic Core", which application is owned by the same common assignee as the present application.